The present invention relates to a process for the treatment of clay-bonded used casting sand wherein said used casting sand is regenerated for use as new sand.
Known in the prior art are processes for the treatment of clay-bonded used casting sand wherein said used casting sand is regenerated for reuse in place of new sand. The processes include treating the old sand in a drum which is rotated about a horizontal axis. During the rotation of the drum the old sand is entrained and separated into sand grains and shell material by the sand grains rubbing against one another under impact stress and shearing stress. The shell material is in the form of dust and the shell material is drawn off by means of a pneumatic dust-removal device to outside the drum.
In these known processes, during the drawing off of the shell dust which comprises a mixture of binding substances and additives, the weight of the used sand originally measured into the drum reduces with time by up to for example 25 wt. %. As is disclosed in German Patent Specification 290 94 08, the stirring and impact action of the old sand in the drum diminishes with the reduction of sand within the drum. Thus, the mutual rubbing action of the sand grains is greatly impaired by the net loss of weight of sand in the drum.
Naturally, it would be highly desirable to provide a process wherein the amount of sand within the drum is maintained at an optimum level with respect to the volume of the drum so as to insure optimum rubbing of the sand grains against each other.
Accordingly, it is a principal object of the present invention to provide a process for the treatment of clay-bonded used casting sand wherein an optimal relationship between the volume of the drum and the quantity of sand in the drum is maintained over the period of treatment of the clay-bonded used casting sand.
It is a further object of the present invention to provide a process wherein the shell of the used sand which is drawn off out of the drum during the batch treatment is compensated for in terms of weight and/or volume by additions of sand material.
Further objects and advantages of the present invention will appear hereinbelow.